In reproducing a digital signal, for example, an adaptive type equalization circuit is employed where an impulse response on a transmission line is estimated for equalizing a playback signal. In more detail, as this type of an adaptive type equalization circuit, for example, as shown in FIG. 5, a playback signal supplied to an input terminal 40 is supplied to a plurality of unit delay means 41 to 44 connected in series. Although the unit delay means are four stages in FIG. 5 for the purpose of simplification, more than ten stages are employed in an actual apparatus. The signals of the input terminals and the output terminals of the unit delay means 41 to 44 are supplied to weighting means 45 to 49, respectively.
The playback signal supplied to the input terminal 40 is supplied to an operation circuit 50 and weighting coefficients C1 to C5 are obtained by estimating an impulse response on a transmission line where LMS (Least Mean Square) algorithm, for example, is employed. The coefficients C1 to C5 obtained in the operation circuit 50 are supplied to the weighting means 45 to 49 and respective weightings are performed for the signals from the unit delay means 41 to 44. Further, the signals from the weighting means 45 to 49 are summed in an adder 51 so that equalization of the playback signal is performed wherein an equalized signal is obtained at an output terminal 52.
By the way in recording/reproducing a digital signal, it was devised that means for taking out a playback signal is provided, for example, without performing tracking control at the time of playback, for example, by recording while an address is added for each recording unit, and repeatedly reproducing its recording track twice or more to extract only recording units that are correctly reproduced, whereby reconstructing the playback signal according to the address. With this means, a structure for the tracking control is not necessary and it is not necessary to record a control signal on a recording medium for that control and the like, whereby recording/reproducing a digital signal can be performed with a simple structure.
In FIG. 6 in more detail, analog signals from a video/audio signal source 61 of a video camera and the like are converted into digital signals in an analog to digital converter (ADC) 62 to be supplied to a compression/expansion circuit 63. A signal supplied to the compression/expansion circuit 63, a buffer controller 64, and a buffer memory 65 is compressed by a certain degree. Further, this compressed signal is supplied to a modulation/demodulation circuit 66 using error correction codes (ECC) and the modulated signal is supplied to magnetic heads Ha, Hb disposed on a rotating drum 68 via a recording/playback circuit 67.
Meanwhile a system controller 70 controlling the entire apparatus is provided such that the compression/expansion circuit 63, the buffer controller 64, the modulation/demodulation circuit 66, the recording/playback circuit 67 and the like are controlled according to a situation, respectively, and communication is performed between the system controller 70 and a mechanical controller 71 at the same time such that driving means 72 such as a motor (M), for example, which transfers a magnetic tape 69, is controlled. In this way the signal from the recording/playback circuit 67 is recorded on the magnetic tape 69 such that the signal forms a diagonal track transferred along the peripheral face of the rotating drum 68.
Further, in the magnetic heads Ha, Hb described above, for example, the azimuth angles of the respective magnetic gaps are set so as to be mutually and oppositely different from the angle perpendicular to the rotational direction of the rotating drum 68 and the magnetic head Hb is arranged so as to perform recording at a position at which the magnetic head Hb overlaps with a track recorded by the magnetic head Ha. In this way a track pattern, for example, as shown in FIG. 7A is formed on the magnetic tape 69 transferred along the peripheral face of the rotating drum 68. That is, in FIG. 7A, recording/playback in which so-called guard bands between tracks are removed is performed.
In another aspect for the magnetic heads Ha, Hb described above, the azimuth angles of the respective magnetic gaps are set so as to be mutually and oppositely different from the angle perpendicular to the rotational direction of the rotating drum 68, the magnetic head Ha is arranged so as to record the next track at a position that is two track pitches ahead of the track recorded last time and the magnetic head Hb is arranged so as to perform recording at a position that is one track pitch behind the next track recorded by the magnetic head Ha. In this way a track pattern, for example, as shown in FIG. 7B is formed on the magnetic tape 69 transferred along the peripheral face of the rotating drum 68.
As seen in FIG. 7B, recording tracks Ta1, Ta2, . . . are first recorded every other track by the magnetic head Ha with a wide width and then on the boundary parts of those recorded tracks, recording tracks Tb1, Tb2, . . . are recorded by the magnetic head Hb. Accodingly even when pairing of the magnetic head Ha, Hb, fluctuation caused by relative positional relationship between the magnetic heads, peripheral fluctuation, fluctuation of the bearing itself or the like occurs, the intervals of the recording tracks Ta1→Tb1, Tb1→Ta2 can be always maintained at predetermined intervals and a prescribed track pattern is formed on the magnetic tape 69.
Accordingly, in any of the track patterns of FIGS. 7A, 7B, the azimuth angles of the magnetic gaps are different as described above, so that it is possible to reduce cross talk from the adjacent tracks by performing playback by the magnetic heads of the corresponding azimuth angles during the time of playback. Thus, recording/playback of a high recording density in which the so-called guard bands between tracks are removed can be performed. For such track pattern in which the guard band is removed, for example, a playback signal can be obtained without performing tracking control during the time of playback.
In more detail, in the apparatus described above, recording is performed, for example, one track each for one rotation of the rotating drum 68 by the magnetic heads Ha, Hb alternately. On the other hand, playback is performed, for example, by two tracks each for one rotation of the rotating drum 68 by magnetic heads Hc, Hd disposed on the rotating drum 68. In this way, each recording track recorded by the magnetic heads Ha, Hb is reproduced two times each by the magnetic heads Hc, Hd. Here, the magnetic heads Ha, Hb are provided at an angle rate of 45 degrees with respect to the circumference of the rotating drum 68, and the magnetic heads Hc, Hd are provided at an angle rate of 180 degrees.
Supplying a signal and taking out a signal are performed in the recording/playback circuit 67 for the magnetic heads Ha to Hd, for example, as shown in FIG. 8. Actually, for one rotation of the rotating drum 68 shown in FIG. 6, recording is performed by the magnetic heads Ha, Hb during the time of recording as shown in FIGS. 8A and 8B. On the other hand, during the time of playback, playback is performed by the magnetic heads Hc, Hd as shown in FIGS. 8D and 8E. Thus, the recording track recorded by one track each for one rotation of the rotating drum 68 is reproduced by two tacks each for one rotation of the rotating drum 68.
Accordingly, the recording track recorded by the magnetic heads Ha, Hb is reproduced two times each by the magnetic heads Hc, Hd. Then, for example, in recorded digital data, a certain address or the like is provided for each recording unit such that, for example, only the recording units which are correctly reproduced can be extracted from playback signals reproduced two times each to reconstruct digital data. There, such reconstruction of digital data can be performed, for example, by the cooperation of the buffer controller 64 and the buffer memory 65 at the same time as demodulation with error correction is performed in the ECC modulation/demodulation circuit 66.
Then, the digital data reconstructed in the modulation/demodulation circuit 66 are supplied to the compression/expansion circuit 63 such that expansion for restoring the compression performed during the time of recording is performed. Further, an expanded digital signal is converted into an analog signal in a digital to analog converter (DAC) 73 and analog signals of, for example, video and audio signals are taken out. The obtained video and audio signals are supplied to a display device 74 such as a television receiver or the like. Thus, recording and reproducing of, for example, video and audio signals by digital data are performed.
Accordingly, with the present apparatus, a track pattern of a high recording density in which the so-called guard bands between tracks are removed is formed during the time of recording and each recording track is reproduced two times each such that only a recording unit that is correctly reproduced is extracted during the time of playback whereby it is not necessary to perform the so-called tracking control especially during the time of playback. Further, by reconstructing recorded units that are correctly reproduced, for example, according to addresses, recording and reproducing digital data can be performed excellently by an extremely simple structure.
However, in such a playback apparatus in which the tracking control is not performed, a playback signal is not always maintained more than a predetermined level and when tracking is deviated, the level of the playback signal is lowered, so that it happens the signal to noise ratio (S/N) becomes extremely deteriorated. Thus, when such a playback signal is supplied, for example, to the adaptive type equalization circuit as shown in FIG. 5, for example, the operation or the like at the time of obtaining the weighting coefficients C1 to C5 for estimating the impulse response described above in the operation circuit 50 malfunctions due to noises and there is a fear that erroneous coefficients C1 to C5 of weighting are formed.
Although such malfunction due to noises also occurs in a normal playback apparatus, serious malfunction does not occur in a normal operation since noises occurred sporadically are restored by normal signals the absolute value of which is great. However, in the playback apparatus in which the tracking control is not performed as described above, it is recognized that continuous noises occur frequently based on the system and it is not possible to avoid malfunction in the adaptive type equalization circuit described above. Consequently, an adaptive type equalization circuit is considered not to be adopted in a conventional playback apparatus in which the tracking control is not performed.
Meanwhile, when the level of a playback signal temporarily decreases due to clogging of a playback head or the like, the intermediate to the high frequency range component of a playback signal decreases so that the envelope becomes small, and in such a case, if the weighting coefficients of an adaptive type equalization circuit are not changed rapidly, there is a fear that the error rate is quickly deteriorated. In another case where for example a head in which Barkhausen noise (discontinuous fluctuation in the output) occurs is employed, there is a fear that the amplitude of a playback signal frequently fluctuates. A conventional adaptive type equalization circuit cannot appropriately cope with such fluctuation.
The present application is developed considering such points and the problem to be solved is that in a conventional apparatus there is a fear that an erroneous coefficients of weighting are formed in an adaptive type equalization circuit, for example, in a case where continuous noises occurs frequently, that an appropriate countermeasure cannot be taken for a temporal decrease in the level of a playback signal and for discontinuous fluctuation in the output, and thus an adaptive type equalization circuit cannot be adopted, for example, in a playback apparatus in which tracking control is not performed.